In accordance with spreading computers and digitizing various kinds of information, both of a total amount and a value of digital data accumulated by a user have been increased. In recent years, in order to save the enormous and important data as a backup, and use the data from plural terminals, an online storage service of storing the data to a storage device which is connected to a user terminal via a network is spreading.
However, when the storage device responds to all of requests for transmitting data from user terminals, all of the exchange of the data is carried out by way of a network. Thereby, a load of the network is increased, a delay in response to each access is increased, and there is a concern that a user's experience is significantly deteriorated.
With regard to the concern, there has been worked out a resolution measure of improving the experience of a user by reducing a network load by connecting a cache device which stores a part of data requested by a user terminal to the user terminal directly or by way of a small-scaled network, and accumulating the data temporarily in the cache device.
When the user terminal receives data, as a method of accumulating the data by the cache device, there is present a cache system, and a data having a high possibility of being requested by a user is accumulated at a cache device by a method shown, for example, in Japanese Unexamined Patent Publication No. 2004-005309 (hereinafter “Patent Document 1”). According to Patent Document 1, a tendency of which data accesses are concentrated is calculated by analyzing an access log of a user terminal, and data are changed such that the data on which accesses are concentrated is accumulated in the cache device. Thereby, the cache device can respond to a number of requests for transmitting data from user terminals, and therefore, the load of the network can be reduced.
According to the method described in Patent Document 1, (popular) contents which can be looked at and listened to by a number of users are stored in a relay server in a service in which plural users look at and listen to images, and the method can divertedly be used also in a method of storing data which can repeatedly be used by a single user at a high frequency to a cache device.
Further, as a method of accumulating data by a cache device when data formed and edited by a user are transmitted, a buffer system or a batch processing is present, for example, data are accumulated, thereafter, transmitted by a method shown in, for example, Japanese Unexamined Patent Publication No. 2006-060631 (hereinafter “Patent Document 2”). According to Patent Document 2, there is provided a means for monitoring an amount of accumulated data such that the data is transmitted after a sufficient amount of data are stored at a transmission buffer part which relays data to be transmitted. Thereby, occurrence of overhead or wasteful retransmission which occurs by transmitting a small amount of data can be restrained, and an efficient data transmission can be carried out.
Further, Japanese Unexamined Patent Publication No. 2003-345709 (hereinafter “Patent Document 3”) discloses a method of achieving high speed formation of a processing of writing data from a user terminal to a storage device, and achieving high speed formation of a processing of reading the data which are written to the storage device by the user terminal by using a cache device.